• Information
  1. Characteristics
  2. Symptoms
  3. Staging and Survival
  4. Treatment

A. Characteristics

1. Uncommon tumor of thymic epithelial cells
   1. Incidence 1.5 per million per year
   2. However, most common (~50%) of anterior mediastinal masses
   3. Typically occurs in age >50 years
   4. Male = Female
   5. Symptomatic in ~40%
2. Thymus-Derived Tumor
   1. Normal T lymphocytes develop in the thymus
   2. Thymus reaches full maturity by age 4-6, then begins involution
   3. Abnormal thymus development leads to immunodeficiency and/or autoimmunity
   4. Thymoma usually arise out of thymic epithelial cells of "thymic remnant"
   5. Histological types A and B and mixed AB
3. Commonly associated with paraneoplastic syndromes

B. Symptoms

1. Mainly anterior mediastinal mass effects
2. Compression of adjacent structures - large blood vessels, trachea
3. Association with Myasthenia Gravis (MG) [2]
   1. About 30% of MG cases are associated with thymomas
   2. Removal of thymus usually leads to significant improvement in MG symptoms
4. Association with Pure Red Cell Aplasia [6]
   1. Thymoma found in ~15% of cases of pure red cell aplasia in adults
   2. Patients present with pallor, fatigue, shortness of breath
5. Association with Hypogammaglobulinemia [7]
   1. Hypogammaglobullinemia occurs in ~10% of thymoma patients
   2. May present with opportunistic infection; serum Ig levels should always be assessed
   3. Good's syndrome is an immunodeficiency associated with thymoma; occurs in ~10%
   4. Good's syndrome may occur after resection also
   5. Syndrome includes both cellular + humoral immune abnormalities: low Ig and lymphopenia
   6. May present with chronic sinus infections, bronchiectasis, pneumonia, infectious diarrhea
   7. Treatment of hypogammaglobulinemia with intravenous Ig (IVIg) as needed
   8. Pneumocystis prophylaxis (and other opportunistic infections) with trimethoprim+ sulfamethoxazole (TMP/SMX)

C. Staging and Survival (5-years) [1]

1. Stage I: completely encapsulated tumor (100% 5 year survival)
2. Stage II: invades adjacent thymus, mediastinal fat, or mediastinal pleura; 98% survival
3. Stage III: invades surrounding structures such as lung, pericardium, great vellels; 90% survival
4. Stage IV
   1. Stage IVA: pleural or pericardial metastases; =70% survival
   2. Stage IVB: lymph node or hematogenous metastases; 50% survival

D. Treatment [3,4,5]

1. Surgical Resection
   1. Mainstay of therapy
   2. Complete resection is a critical prognostic factor
   3. Complete resection often difficult due to sticking of tumors to adjacent structures
2. Induction Chemotherapy
   1. Pre-surgical chemotherapy is recommended for Stages III and IV
   2. Chemotherapy includied cyclophosphamide, doxorubicin, cisplatin and prednisone
   3. Cisplatin + etoposide also provide good response rates, overall survival
   4. Excellent response rates to induction chemotherapy (3 courses)
   5. May be followed by radiation therapy (if tumor necrosis <80%)
   6. Consolidation chemotherapy recommended for patients with non-local disease
   7. Response rates are >50-80%
   8. Note that glucocorticoids + octreotide provide responses in ~30% in metastatic disease
3. Radiation Therapy
   1. Adjunctive therapy for incomplete resection or for local control in general
   2. Adjunctive therapy for partial (<80% necrotic) and complete responses to chemotherapy
   3. Doses are typically 50-60 Gy
   4. Postoperative radiotherapy for Stage III and IV usually recommended

References

1. Wright CD, Fidias P, Choi NC, et al. 2007. NEJM. 356(21):2185 (Case Record)
2. Drachman DR. 1994. NEJM. 330(25):1797
3. Shin DM, Walsh GL, Komaki R, et al. 1998. Ann Intern Med. 129(2):100
4. Loehrer PJ Sr. 1999. Ann Med. 31(Sup2):73
5. Thomas CR, Wright CD, Loehrer PJ. 1997. J Clin Oncol. 17(7):2280
6. Dhaliwal G, Schmidt KE, Gilden DJ, Saint S. 2004. NEJM. 350(1):60 (Case Discussion)
7. Ezzie ME, Janssen WJ, O'Brien JM, et al. 2008. NEJM. 358(1):70 (Case Record)